Manufacture of sulphite pulp



May 29, 1945. G. H. ToMLlNsoN MANUFACTURE OF SULPHITE PULP Original Filed Jan. 26, 1938 2 Sheets-Sheet l wmekovm Lemmi mtnLvm.

ATTORNEY May 29, 1945. G. H. ToMLlNsoN MANUFACTURE OF SULPHITE PULP Original Filed Jan. 26, 1938 2 Sheets-Sheet 2 INVENTOR. georg@ H. 75m/msm? BLQLP h Patented May 29, 1945 MANUFACTURE F SULPHITE George H. Tomlinson, Westmount, Quebec, Canada Original application January 26, 1938, Serial No.

Divided and this application August 14, 1940, Serial No. 352,507

7 Claims. (Cl. 2li-262) The present invention relates to the manufacture of pulp from cellulosic fibrous material by the Iacid or sulphite" process. The cooking liquor ordinarily employed in the sulphite process has as its active reagent mainly an acid sulphite compound of calcium. The general practice. in the sulphite industry is to discharge the residual cooking liquid into nearby streams or bodies of water, thereby polluting the same.

As disclosed in my prior joint Patent No. 2,179,- 456, it has been found possible to burn sulphite pulp residual liquor in a self-sustaining combustion process and recover heat and chemical values. With a calcium base sulphte liquor, the chemicals could be recovered in the form of a dry ash but no economic method is yet known for transforming the calcium compounds recovered into a condition which would permit their reuse in the pulping process.

The use of other acid sulphite compounds has been suggested as a cooking liquor base. If a sodium base residual liquor is burned as aforesaid the chemical solids can be recovered from the furnace in the form of asmelt containing sodium sulphate (NazSOl) and sodium sulphide (NazS). The sulphate is reducible to the sulphide so that the sulphur in the liquor can be reclaimed mainly in the form of the sulphide. The problem however still remains of converting sodium sulphide into sodium bisulphite (NaHSOs) and as yet no method has been developed by which this can be completely accomplished commercially.

Of the bases other than sodium or calcium that might be used as bisulphite-strontium, barium, magnesium, zinc-their relatively high cost and/or scarcity, and the fact that no method has been devised for their recovery, has precluded their commercial consideration. Dolomitic limestone has also been used as the source of the calcium base, so that magnesium in varying amounts, in addition to the calcium, may be present in the cooking liquor. The presence of magnesium compound is particularly beneficial where the residual liquor is concentrated in an evaporator, since the calcium compounds tend to form an insoluble scale, Whereas the magnesium compounds are considerably more soluble. Pure magnesium base sulphite cooking liquor has not been heretofore used commercially because of its much Vgreater cost in the absence of any practical process and apparatus for the recovery of its chemical content.

The main object of my invention is the provision of apparatus adapted for use in a process of manufacturing sulphite pulp from cellulosicilbrous material with a pure magnesium base cooking liquor, and more particularly, to apparatus for efilciently recovering the heat and chemical values in the residual pulp liquor from such a process.

` The various features of novelty which characterlze my invention are pointed out with partic- -ularity in the claims annexed to and forming a part of this specification. For a better understanding of the' invention, its operating advantages and specic objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is a diagrammatic flow sheet of a cyclic pulp process using a relatively pure magnesium base sulphite cooking liquor;

Fig. 2 is a sectional elevation of a preferred recovery furnace construction taken on the line 2-2 of Fig. 3; and

Fig. 3 is a section on the line 3-3 of Fig. 2.

Calcium, barium, strontium, and magnesium are usually grouped as related metals. It is generally believed that the sulphates of such metals when heated in the presence of carbon will normally be reduced to the corresponding sulphides with the liberation of carbon dioxide. This is true for all the elements of this group, with the exception of magnesium, the sulphate of which under certain conditions, has a greater tendency to reduce directly to the oxide, with the liberation of its sulphur content in the form of sulphur dioxide, and without appreciable formation of the sulphide, i. e. in accordance with the following equation:

2MgSO4+C=2MgO+2SOa+COz The magnesium sulphate is thus reduced to magnesium oxide with the release of sulphur dioxide and carbon dioxide. The sulphur atom in both sulphates and sulphonates is hexavalent and the formation of MgO and SO2 from either conipound requires reduction. In spite of the fact that, according to the literature, diiilculty is encountered in carrying out this reaction of Mg804 when the ratio lof sulphate to carbon differs materially from that indicated by the equation above, I have discovered that this tendency of magnesium sulphate and magnesium sulphonate to reduce to the oxide can be used, under certain conditions. in the manufacture of sulphite pulp. Speciiically, when a pure magnesium base4 sulphite liquox` is used. both the base and sulphur content can be substantially completely recovered from the residual liquor in a form suitable for use in an economic cyclic process.

As indicated in Fig. 1, a cooking liquor consisting of a pure acid sulphite compound of magnesium, i. e. magnesium bisulphite, with an excess of sulphur dioxide is supplied to the digester. When the cooking operation is completed, theresidual liquor is separated from the pulp by suitable washing equipment, such as a rotary vacuum filter. The pulp residual liquor with its content of magnesium lignin sulphonate is then neutralized as hereinafter described and delivered to a multiple-effect evaporator wherein it is evaporated to a higher solid concentration, yet one suitable for spraying, such as concentrations of 45 to '70% solids.

With the apparatus hereinafter described, the residual liquor when so concentrated can be successfully burned to a dry ash under self-sustaining combustion conditions and its heat and chemical values economically recovered. The ash produced will consist of a mixture of magnesium oxide (MgO) and magnesium carbonate (MgCOa), as well as a small amount of unreduced magnesium sulphate, depending upon the reduction eiiiciency.

The magnesium oxide, to be of commercial value in a cyclic process, must be recovered mainly in a form in which it will readily react with sulphurous acid. When magnesium compounds are calcined, 'two substantially different types of magnesium oxide can be produced, caustic magnesia and dead-burned magnesia, depending mainly upon the time and temperature conditions employed. For caustic magnesia, the calcination is usually carried out under temperatures approximating 1800 F. A completely deadburned product is produced at temperatures approximating 2700" F. 'I'he product at the lower temperature is quickly soluble in weak acids, such as sulphurous acid, and at the higher temperature, the product is only soluble with difficulty in strong acids, and is almost, if not entirely, insoluble in sulphurous acid. With calcination temperatures above 1800 F. lthe reactivity of the product diminishes down to the point at which it is completely' dead-burned.

In addition to the effect of temperature, the time element must also be considered in the production of magnesia. Even aft temperatures approximating 1800 F., the reactivity can be seriously impaired if the magnesia is exposed to such a temperature for too long a time. The smaller the particle size, the greater the impairment for a given period. Above 1800 F., unless the time element is extremely short, the chemical reactivity of the product is seriously affected.

A large percentage of the solid content of the residual liquor is in the form of carbon which must be eliminated during the recovery operations to avoid subsequent contamination of the pulp when the recovered ash is reused and to fully utilize the heat value of the liquor. Recovery of a high percentage of the sulphur content of the liquor is also essential for an economic cyclic process. 'I'he sulphur content is initially released as sulphur dioxide (SO2) which is relatively unstable in the presence of oxygen and rtends to form other sulphur compounds, such as S03. While any trioxide in the heating gases formed can be recovered in an absorption tower, it would combine to form sulphate and therefore increase the dead load of chemical circulating in the system.

An economic cyclic process of making a pure magnesium base sulphite pulp therefore requires an eflicient recovery of the heat and chemical values of the residual liquor, the recovery of the magnesium compounds with a high percentage of magnesio., high reactivity and free from carbon, continuous removal of calcium and other inorganic impurities, and the recovery of the sulphur from the heating gases in the form of sulphur dioxide. It has been found however, that the recovery furnace conditions desirable for obtaining some of these results are not suitable for obtaining others. For example, th e highest percentage of reduction tends to occur when a high temperature highly reducing atmosphere is maintained in the furnace. However, high temperature conditions are not suitable for obtaining, a highly reactive magnesia, nor is a highly reducing atmosphere suitable for complete combustion of the carbon. Similarly the percentage of SO2 converted into S03 tends to increase as the `amount of excess air present increases and as the temperature decreases.

`'In accordance with my invention, the concentrated magnesium basey sulphite residual liquor A is successfully burned under self-sustaining combustion conditions and the heart and chemical values recovered in a'desirable form. I have found that it is preferable to burn the liquor entirely in suspension in a two-stage recovery furnace operation. For suspension burning of the magnesium base sulphite residual liquor I prefer to employ a recovery furnace in which the primary combustion and reducing zone is located in a refractory Walled chamber and the secondary combustion zone in a separate water cooled chamber so that the most suitable furnace conditions can be readily maintained for self-sustaining combustion and the production of a chemical ash having a high reduction, high reactivity and a low carbon content, and the recovery of sulphur as sulphur dioxide. The concentrated residual liquor is finely atomized on entering the primary combustion and reducing zone, either by an impinging jet of steam or other atomizing uid. The furnace employed is designed as to size, shape and heat absorption surface to effect a normal mean temperature in the primary combustion and reducing zone approximating 1800 F. with the designed normal rate of firing of the sulphite liquor. Combustion air is supplied in regulable quantities and proportioned between the primary combustion and reducing zone and the secondary combustion zone to provide the desired highly reducing atmosphere in the first zone and a slightly oxidizing atmosphere in the second zone. The usual forced and induced draft fans, pumps, control equipment, and other auxiliaries are employed. In starting up the furnace is first preheated to a predetermined temperature by auxiliary fuel. The finely divided liquor particles on exposure to the furnace conditions in the primary combustion and reducing zone pass rapidly through the successive stages of dehydration distillation and combustion in transit, burning tl a light chemical ash, mainly in the form of small light cenospheres and flakes which remain suspended in the combustion gases and are removed from the furnace entirely by flotation.

Since the magnesium salts are neither fusible nor volatile at such temperatures, chemical losses in the furnace due to fume formation are avoided. The furnace conditions described are conducive collecting hopper 18 is arranged below the front toa rapid reduction of .the magnesium sulphate to magnesium oxide and for the release of the sulphur as sulphur dioxide. The stronglyreducing atmosphere maintained in the primary combustion and reducing zone also minimizes the conversion of the sulphur dioxide released to sulphur trioxide. The rapid combustion of the organic material and immediate flight of the ash formed in the gas stream limits the time of exposure of the ash to the high temperature conditions in this zone and does not materially affect the reactivity of the ash. The highly reducing atmosphere and the normal presence of a small amount of unburned carbon in the ash particles due thereto also appears to aid in maintaining a high ash reactivity.

Unburned carbon in the ash is burned out while the ash is passing through the secondary combustion zone. Due to the use of a water cooled chamber for this zone, a normal mean temperature approximating 1950 F. can be readily maintained therein, thereby minimizing the eect on the ash reactivity and the formation of sulphur trioxide in this zone. The ash-laden gases on leaving the secondary combustion zone flow through suitable heat absorbing and ash separation apparatus.

With the liquor burned in suspension to a light ash in an atmosphere of upilowing heating gases in the furnace chamber, little, if any, of the ash will drop to the bottom of the chamber and sub-V stantially all of the ash will rapidly pass out with the heating gases. All of the liquor particles will be subjected to substantially the same conditions while in the furnace, contributing to stable operation and uniform removal of the ash. Under these conditions the period during which the liquor particles and resulting ash is exposed to the furnace temperature conditions will be extremely short and dead-burning virtually eliminated.

I have illustrated in Figs. 2 and 3 an experimental recovery furnace in which the described method of burning magnesium base sulphite residual liquor in suspension has been successfully carried out. The recovery furnace shown consists of a refractory walled furnace including a front wall 60, rear wall 5 l, and side walls 62, with the space therebetween divided into serially connected elongated gas passes 53, 65, 65, and 66 by a vertical bridge wall 69, a vertical partition 61, and a horizontal arch 68. The pass 68 is horizontally elongated between the arch 68 and the underside of the horizontally arranged fire tube boiler 10. The passes 63 and 6ft are thus entirely refractory Walled. while the passes 85 and 86 have a substantial amount of water cooled wall area.

A pair of steam atomizing liquor nozzles 1i are arranged adjacent to the upper part of the front wall 60 at laterally spaced points. Primary air supply pipes 12 open through the front wall above the corresponding nozzles 1| for supplying combustion air to corresponding refractory hoods 13 arranged to direct the primary air downwardly between the streams of atomized liquor discharged from the nozzles 1l and the front wall 60. Additional primary air supply pipes 'Il are located in the lower part of the front wall, and directed downwardly to direct a stream of primary air rearwardly across the floor 15, which is air cooled, to sweep up any ash depositing thereon. A pair of vertically spaced horizontally arranged secondary air pipes 16 extend across a pair of openings 11 in the bottom of the partition 61 with the discharge openings in the pipes oppositely directed to cause an intimate mixture oi' the secondary air and gases passing through the openings 11. A

end of the pass 66 which extends beyond the/front wall 0l. Heating gases from the pass 66 flow over the hopper 18 and turn upwardly into the front end of the fire tube boiler 10, passing through the boiler tubes 80 to a gas exit flue 8l at its rear end. The test apparatus was constructed with the approximate dimensions indicated in Figs. 2 and 3.

In one ring run in the described test apparatus a pure magnesium base sulphite residual liquor having a concentration of 32.6 Baum at 62 F. was supplied to the liquor nozzles 1l at a. pressure of 16 lbs. per square inch gage and a temperature of 170 F. The liquor atomizing fluid was saturated steam at a pressure of 40 lbs. per square inch gage. The residual liquor had a solid content of with an ultimate analysis of Per cent- Carbon 45 Hydrogen 4.5 Sulphur 4 Ash 13 Oxygen-l-nitrogen (by difference) 33.5

The heat value of the liquor on a dry basis was '1600 B. t. u./lb. The residual liquor was supplied to the nozzles 1l at the rate of 3200 lbs/hr. Combustion air was supplied to the primary air pipes 12 'and 1I and secondary air to the pipes 16 at a temperature of 210 F., with the total supply of air to the furnace ranging from 102 to 116% of the theoretical air requirements for complete combustion of the organic combustible constituents of the liquor. 70% of the air was supplied through the pipes 12, 15% through the pipes 14 and 15% through the pipes 16. A slight negative pressure was present in the furnace.

In operation the residual liquor was downwardly directed in finely atomized streams by the nozzles 1l and burned in suspension while in a U- shaped flame path in the pass 63 and while in the downflow pass 54. These passes formed the primary combustion and reducing zone or chamber of the unit, and the temperature conditions therein were as indicated in Fig. 2. As the ash laden furnace gases passed through the openings 11, the additional combustion air supplies at this point caused further combustion in the water cooled passes 65 and 86 of any unburned carbon present. The furnace temperatures in the secondary combustion zone or chamber formed by the passes 65 and 85 were maintained within the desired range by the relatively large amount of water cooled surface effective therein as indicated by the temperatures noted in Fig. 2. The steam production in the various test runs averaged approximately 2 lbs. of steam per pound of liquor fired. The flue gases had the following average analyses:

Per cent CO2 17.7 O 2.4 SO2 6 The average time of' travel through the test unit under the described conditions was computed to be between three and four seconds.

The ash was carried out of the furnace by flotation in the furnace gases and separated in a cyclone type dust collector. An analysis of the ash showed a reduction of 93 to 941/ a mean reactivity slightly higher than that of the commercial caustic magnesla used in making the original cooking liquor, and a carbon content of from zero to .5%. The ash produced was mainly in the form of light cenospheres and flakes having a density of from three to eight lbs. per cu. ft., the density increasing as the reactivity decreased.

The ash recovered in the separating and collecting apparatus is advantageously treated with water to form anralkaline liquor in the solution tank which is divided into two parts on leaving the solution tank. One portion is fed back into the residual liquor prior to its evaporation for the purpose of neutralizing its acid content. By this step, loss of sulphur during the evaporation step is eliminated and necessity for acid resisting material for the evaporator is minimized.

'Ihe other portion of the ash is supplied to the top of the absorption towers, as indicated in Fig. 1. The difficulties of recovering low percentages of SO2 in the flue gas are largely eliminated when the recovered magnesia is sufficiently reactive. The magnesia combines with the sulphur dioxide in the ascending gases to form magnesium sulphite and bisulphite. The flow of gas absorbing liquor is so regulated and controlled through the absorption towers that only a negligible amount of sulphur escapes in the gases. In test runs with the apparatus described, gas analyses showed that over 90% of the sulphur content of the residual liquor was recovered by the absorption towers. Not only are the sulphur constituents of the gases recovered in the absorption towers, but also any solids remaining in the gases. 4The liquor with its sulphur content increased is Withdrawn from the bottom of the second absorption tower, while the clean gases pass through an induced draft fan to the stack.

In view of the necessity for permitting the ash to remain in the furnace chamber for only a brief period to avoid dead-burning thereof and the desirability of limiting the amount of combustion air to the furnace, a small amount of unburned carbon particles may be carried out with the ash in the heating gases. Such impurities would be immaterial in the portion of the ash employed for neutralizing the liquor before evaporation, but must be eliminated before reuse of the recovered chemicals in the digester to avoid contamination of the pulp. Accordingly, the liquor withdrawn from the second absorption tower is passed through a suitable filter, such as a. sand filter. to remove any carbon particles present in the liquor.

The filtered liquor is delivered to a storage place, and as required is supplied to the cooking acid tank. Magnesia losses in the system are made up by introducing magnesium sulphate into the liquor before burning or by introducing magnesium carbonate or oxide along with the ash. When the sulphate is employed for this purpose it also assists at the same time in maintaining the sulphur balance. The burning of a small amount of sulphur is usually required however in order to maintain this condition, and this may be added in an absorption tower before delivery of the sulphite liquor to the cooking acid tank. The sulphite liquor formed is fortified in the usual way by introducing into it the sulphur dioxide relieved and recovered froml the digester during the cooking operation. The liquor is then ready to enter upon a fresh cycle.

rI'he substitution of a magnesium base involves no change in the usual sulphite cooking practice. In producing a ton of sulphite pulp at least a similar quantity of material is dissolved out of the wood and remains in the liquor. At the same time approximately 200 pounds of sulphur along with about 300 pounds of the base when calculated as calcium carbonate remain in the solution and are normally lost. By means of the described apparatus a high percentage of both the sulphur and base can be directly recovered for reuse in the pulping process. At the same time the combustion of the organic constituents of the residual liquor will produce an amount of steam substantially in excess of the requirements of the pulping process including the recovery step. The magnesium base pulp produced has been found to be equal to and in some respects superior to calcium base sulphite pulp from the same woods. For the same ratio of total sulphur to combined sulphur in the cooking liquor, the magnesium base pulp has been found to have a slightly better color and to require a lesser amount of bleaching material.

It can therefore be seen that this process offers substantial economic advantages in addition to providing a complete solution to the problem of residual sulphite liquor disposal.

While in acordance with the provisions of the statutes I have disclosed herein the best embodiments of my invention now known to me, those skilled in the art will understand that changes may be made without departing from the spirit of the invention covered .by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

This application is a division of my prior application Serial N o. 186,938, filed January 26, 1938, which matured as U. S. Patent No. 2,285,876 on June 9, 1942.

I claim:

1. Apparatus for the recovery of chemicals in a dry condition and heat from waste liquor containing inorganic chemicals and combustible organic matter comprising in combination walls defining a furnace chamber having a normally closed bottom section devoid of smelt outlets and a gas outlet in the upper part thereof, means for introducing and spraying the waste liquor into said furnace chamber, said furnace chamber and sprayingv means being constructed and arranged for burning the waste liquor in suspension therein while passing towards said gas outlet to yield combustion gases and a dry chemical ash in suspension, means for controlling the atmosphere in said furnace chamber including an air inlet adjacent said spraying means and an air inlet adjacent said furnace chamber bottom and arranged to sweep up ash from said furnace chamber bottom, whereby the combustion gases leaving said gas outlet contain in suspension substantially all of the chemical ash produced in said furnace chamber, an unobstructed vertical downow gas passage for ash-laden combustion gases joined to said furnace chamber by said gas outlet, and the eil'ective gas flow area of said vertical gas passage being constructed and relatively proportioned to provide a gas velocity therein suiiicient to maintain said chemical ash in suspension in said combustion gases.

2. Apparatus for the recovery of chemicals in a dry condition and heat from Waste liquor containing inorganic Ychemicals and combustible organic matter comprising in combination walls defining a furnace chamber having a normally closed bottom section devoid of smelt outlets and a gas outlet in the upper part thereof, means for introducing and spraying the waste liquor into said furnace chamber, said furnace chamber and spraying means being constructed and a1'- ranged for burning the waste liquor in suspension therein while passing towards said gas outlet to yield combustion gases and a dry chemical ash in suspension. whereby the combustion gases leaving said gas outlet contain in suspension substantially all of the chemical ash produced in said furnace chamber, an unobstructed vertical downow Sas passagedor ash-laden combustion gases r-joined to said furnace chamber by said gas outlet, regulable air inlet means for controlling the atmosphere in said furnace chamber, means dening a second vertical gas passage connected to and receiving ash-laden combustion gases from the lower end of said rst gas passage, means for introducing additional combustion air into one of said vertical gas passages, the effective gas iiow areas of said Vertical gas passages being constructed and relatively proportioned to provide a gas velocity therein sufficient to maintain said chemical ash'in suspension in said combustion gases.

3. Apparatus for the recovery of chemicals in a dry condition and heat from waste liquor containing inorganic chemicals and combustible organic matter comprising in combination walls defining a vertical furnace chamber having a normally closed bottom section devoid of smelt outlets 'and a gas outlet in the upper part thereof, means for introducing and spraying the waste liquor downwardly into said furnace chamber, said furnace chamber and spraying means being constructed and arranged for burning the waste liquor in suspension therein while passing through a U-shaped flame path to said gas outlet to yield combustion gases and a dry chemical ash in suspension, means for controlling the atmosphere in said furnace chamber including an air inlet adjacent said spraying means and an air inlet adjacent said furnace chamber bottom and arranged to sweep up ash from said furnace chamber bottom, whereby the combustion gases leaving said gas outlet contain in suspension substantially all of the chemical ash produced in said furnace chamber, an unobstructed vertical downflow gas passage for ash-laden combustion gases joined to said furnace chamber by said gas outlet, means defining a second vertical gas passage connected to and receiving ash-laden combustion gases from the lower end of said first gas passage; means for introducing combustion air into one of said vertical gas passages, the effective gas iow areas of said vertical gas passages being constructed and relatively proportioned to provide a gas velocity therein sufficient to maintain said chemical ash in suspension in said combustion gases, and a heat exchange device constructed and arranged to rapidly reduce the temperature of said ash-laden combustion gases.

4. Apparatus for treating waste residual cooking liquor from the digestion of cellulosic brous material comprising in combination walls defining a vertical furnace chamber, an outlet for products of combustion and a downwardly directed spray means for said waste liquor oppositely arranged in an upper port n of said chamber, means admitting primary combustion air to the chamber including an inlet adjacent said spray means, an inlet adjacent the floor thereof so located as to direct a gaseous current against falling particles resulting from the sprayed liquor and to cause combustion of organic constituents thereof in suspension and in a U-shaped flame path from said spray means toward said outlet, an unobstructed vertical downflow passage for the products of combustion joined to said furnace chamber by said outlet, a substantially unobstructed vertical upfiow passage opening from said downiiow passage,.secondary air inlet means in said upow passage, the effective gas iiow areas of said vertical passages being constructed and relatively proportioned to provide a gas velocity therein sufficient to maintain combusted solid particles in suspension.

5. Apparatus for treating waste residual cooking liquor from the digestion of cellulosic iibrous material comprisingin combination walls denning a furnace chamber having a normally closed bottom section devoid of smelt outlets and an outlet for ash-laden combustion gases in the upper part thereof, spray means for introducing said waste liquor into said furnace chamber, means admitting primary combustion air into said furnace chamber including an air inlet adjacent said spray means so located as to cause combustion of the organic constituents of said sprayed liquor in suspension in a flame path from said spray means toward said outlet and the combustion gases leaving said outlet to contain in suspension substantially al1 of the ash produced in said furnace chamber, an unobstructed vertical downilow passage for the ash-laden com'- bustion gases joined to said furnace chamber by said outlet and having a wall structure arranged to substantially shield said downflow passage from said furnace chamber, a substantially unobstructed vertical upow passage opening from said downfiow passage, secondary air inlet means in one of said vertical passages, and the eective gas iiow areas of said vertical passages being constructed and relatively proportioned to provide a gas velocity therein suilicient to maintain the ash particles in suspension.

6. Apparatus for treating waste residual cooking liquor from the digestion of cellulosic brous material comprising in combination walls defining a furnace chamber having a normally closed bot-` tom section devoid of smelt outlets and an outlet for ash-laden combustion gases in the upper part thereof, spray means for introducing said waste liquor into said furnace chamber, means admitting primary combustion air into said furnace chamber including an air inlet adjacent said spray means so located as to cause combustion of the organic constituents of said sprayed liquor in suspension in a llame path from said spray means toward said outlet and the combustion gases leaving said outlet to contain in suspension substan tially all of the ash produced in said furnace chamber, an unobstructed vertical downiiow passage for the ash-laden gases joined to said iurnace chamber by said outlet, a substantially unobstructed vertical upow passage opening from said downflow passage, the effective gas ow areas of said vertical passages being constructed and relatively proportioned to provide a gas velocity therein sufllcient to maintain the ash particles in suspension, and an external ash separating device arranged to receive said ash-laden combination gases.

7. Apparatus for treating waste residual cooking liquor from the digestion of cellulosic fibrous material comprising in combination walls defin- ,ing a vertically elongated furnace chamber having a normally closed bottom section devoid of smelt outlets and an outlet for ash-laden combustion gases in the upper part thereof, spray means for introducing said waste liquor into said furnace chamber, means admitting primary combustion air into said furnace chamber including an air inlet adjacent said spray means so located as to cause combustion of the organic constituheat exchanging device having gas iiow passages 10 CII in the path of travel of said combustion gases from said upilowV passage, the eirective gas iiow areas of said vertical passages and fluid heater being constructed and relatively proportioned to provide a gas velocity therein sumcient to maintain the ash particles in suspension, and an ash separating device arranged to receive the ashladen combustion gases from said heat exchanging device.

GEORGE H. TOMLINSON. 

